A. Technical Field
This application relates to optical signal power control, and more particularly, to the control of variable gain amplifiers to provide constant gain on each channel within an optical signal.
B. Background of the Invention
The importance of optical networking technology in today's society is well understood. Optical networks allow large amounts of information to be transmitted at high data rates across very long distances. In optical long haul scenarios, multiple channels or wavelengths are typically multiplexed together and inserted into a fiber optic cable that spans a long distance. The optical signal, comprising multiple wavelengths, propagates within the fiber optic cable until its destination is reached. This signal may then be demultiplexed and the individual wavelengths further processed.
It is oftentimes important that the optical power levels of the wavelengths or channels have a particular power profile. For example, it is commonly preferred that each wavelength within a wave length division multiplexed signal have the same power level. These power levels may be controlled according to span looses and gain values of optical amplifiers along an optical link. Optical spans typically have optical amplifiers that are inserted within the optical fiber. An optical amplifier applies a gain to each wavelength within an optical signal resulting in an output power level for each wavelength.
The per channel power and total power of all signal channels should be controlled at both an input and output of a network node and across optical fiber spans. These nodes include, but are not limited to, EDFAs, optical add/drop nodes, data transmit and receive nodes and dispersion compensation nodes.
Controlling optical channel power is further complicated when the number of optical channels within an optical link varies overtime. In particular, if the number of channels within an optical signal changes, then the gain on one or more optical amplifiers within the link may need to be varied in order to maintain a preferred output optical power on each of the channels. Referring to FIG. 1, an optical link 100 is shown including a head end node 110 and a far end node 150. The head end node 110 is coupled to the far end node 150 by fiber optic cable and multiple optical amplifiers. In this instance, there is a first optical amplifier 120, a second optical amplifier 130 continuing to an Nth optical amplifier 140.
In order to properly manage this link, the power levels on both the input and output of each of the optical amplifiers (120, 130, 140, 150) should be controlled. As mentioned above, these power levels may incur penalties when the number of optical channels suddenly changes and the amplifiers are unable to quickly respond. Many systems also use only fixed gain amplifies which require that all the span losses have to be of a predetermined loss value. The use of fixed gain amplifiers makes power management on the link 100 even more difficult. For example, certain systems may use attenuating pads within an optical link to match the span loss to the fixed gain of the amplifiers.
Accordingly, what is needed is a system and method that address the above-described shortcomings.